8/8/12 6:40 AM EDT

Although 40 percent of voters now say they hold a favorable opinion of the former Massachusetts governor — virtually unchanged from May — those holding negative views of him ticked higher in the new survey, from 45 percent to 49 percent.

Meanwhile, President Obama remained in positive territory on that measure, with 53 percent of voters reporting favorable opinions of him. Only 43 percent say they feel unfavorably toward him. …

Romney’s inability to gain on Obama since then may be a sign that his image has been damaged by summer stumbles, including new attention on his tax returns and an overseas trip that included several gaffes. …

Critically, independent voters now hold their favorable views of Obama more strongly than they do of Romney. More independents view Obama favorably than unfavorably, by a margin of 53 percent to 40 percent. Their opinions of Romney were nearly reversed, with 37 percent viewing him favorably and 50 percent unfavorably.

Candidate errors presumably play a role in these numbers, but you also can't underestimate the impact of tens of millions of dollars in negative ads from the Obama campaign and super PAC. The tricky thing is that the top line numbers in the presidential race remain close, so you have to ask: does that mean voters are willing to vote for Romney even if they don't like him, or has Obama successfully poisoned the well with undecided voters so that they will break against the challenger in November?